Signaling system



Patented Aug. 23, 1927.

. iran STATES. PATENT OFFICE..

AUSTENM. CURTIS, or nAsT ORANGE, NEW JERSEY, AssrGNonTo BELL TELEPHONE v Lascaaronrns, monarca-aaien, er Nnw Yemen' Y., A CORPORATION on NEW YORK.

SIGNALING SYSTEM.

Application filed December` 12, 1925. Serial' No. 75,015.

This invention relates to signaling and to' 5 circuit for connection to the amplifier input or ont-put, especially where disturbance due to undesired currents, such for instance as currents resulting from ,the tendency of the amplifier to oscillate and from voltages Iinduced in the circuitby extraneous sources, should be guarded against. l Y f A In accordance with the inventiom'signals may be transferred between the amplifier and the circuit, for instance over a twin conductor cable balanced as regards the impedances to earth of its conductors, without disturbing such balance or introducing serious transmission loss, and at the same time the amplifier is Veffectively stabilized and any necessity for employing a connecting transformer isavoided. Such al transformer might be difficult to. design and construct where the signal wave contains current components of very low frequencies, as is thel case inthe transmission of telegraph signals over a long submarine cable. It is also ank object of the invention to reduce disturbances in transferring signals or the like through two circuits between which is interposed an amplifier and which are eX- posed to interference from extraneous electric fields. f

In transmitting signals betweenha space discharge amplifier and a circuit which is balanced with respect to the impedances of its two sides to earth, the-ampliier isstabilized with relation to its surroundings, for yfrequencies at which otherwise it might oscillate, by earthing the amplifier cathode through a. connection having impedance sufiiciently low to prevent such oscillation; and at thesame time, the balance of the circuitis maintained by interposing an electromechanical relay between theramplifier and the circuit. Signals are transmitted between the circuit and another circuit, such as a submarine cable with its balancing circuit, through the amplifier and the electroechanical relay, and imbalance between the cable and its balancing circuit is avoided by employing a transformer to connect the cable and its balancing circuit to the ampiiiier or by balancing the impedance which earths the cathode and the cablel conductor, or its balancing return circuit conductor,

vention in submarine cable telegraphy,,al-

though is lnot limited to such application'. Fig. 1 4is a. circuit diagram ofaform of the invention employing a transformer for con-v necting the cable and its balancing circuit to the amplifienvas referred to above, and

Fig. 2 shows diagrammatically aform of the invention in` kwhich similar connensers connected from earth to the cable and its' balancing circuit, respectively, as referred te above.y y v i l i The cableA systems herein descrihedare adapted for yuse with submarine cables of such, great length that signals arrive from the cable greatly attenuated and distorted.; In order to retransmit these signals it isl therefore necessarynto amplify them and eorrectthe distortion by snitable shaping apparatus and it will frequently be found essential to usel efficient lmeans Vof minimizing the effect of extraneous electrical fields acting on thecable or on the secondv circuit to which signals' aretransmitted in order toypreventthe signalsufrom being mashed by theV induced disturbances. may, however, become ofuse inother types of signaling systems` as the severity of operating conditionsY increases.

In the drawing, 1A is intended to represent a cable,:for example, a .loaded submarine cable having `large ,distributed capacity, in-v ductance and resistance, and2 is intended to represent a 'direct amplifying type of electric space,dischargefamplilier for receiving telegraph signals from the cable 1 and transmitting lthem by lmeans of.relays 11 and 11' through circuits 1,0 and 10 to receiving apparatus 12." They term direct amplifying type is'used in the specification andl claims to-y define an amplifier that increases `the energy of an electric' wave Such means without shifting or converting the frequency of the wave before, after, or during the amplification.

To provide for multiplex transmission, the receiving apparatus 12 may be of a well known type employing a rotary distributor (not shown) having a brush movable over a solid ring and a ring of segments for separating a plurality of messages which have been combined by a similar rotary switching means (not shown) at the sending end of the cable, the segments of the receiving distributor being connected to correspond with receiving devices (not shown), to distribute the messages to the receiving devices, which may be siphon recorders, such as the recorder indicated at 12 in Fig. 2, or may be any desired type of receiving or relaying devices. The receiving apparatus 12 may also include means (not shown) responsive to signals transmitted from the sending end of cable 1 through the cable 1, the amplifier 2, a relay 11 and a circuit 10 to maintain the receiving distributor in synchronism with the rotary switching device at the sending end of the cable 1. This synchronizing apparatus may be, for instance, of the tuning fork and phonic wheel type described in detail in U. S. patent to Spencer 1,333,000, granted March 9, 1920. he windings of relay 11 are shown connected in serial relation to those of relay 11 and to those of a third relay 21 which may be employed to operate a siphonvrecorder or the like (not shown) or means (not shown) which may be local to the amplifier 2 for influencing the potential of a grid of the amplifier in such a manner as to reduce zero wander in the system as disclosed in my application Serial No. 106,355, filed May 3, 1926. Means are described hereinafter whereby the current in the windings of each relay may be adjusted inde pendently of the current in the windings of the other relays.

rihe cable 1 comprises a single core section 3 terminated in a'twin core section 4. One core 5 of a twin core section 4 is connected at one end to the single core section 3 and at the other end to one terminal of signal receiving apparatus which comprises amplifier 2 ano which will be presently described. The other terminal of the receiving apparatus is connected to one end of the second core 6 of the twin core section 4, the other end of core 6 being connected through a resistance 7 to a conductor in contact with the sea water, to furnish an earth connection. As shown, the resistance is connected to the cable armor wires 8 at point 9, a conventional grounding symbol being employed in the drawing to indicate that the armorwires are earthed. The core 6 together with the network 7 grounded at the point 9 constitutes a cable balancing re portion of the cable which lies in shallow' water. The twin core section of the cable is terminated in the connection through the resistance to the sea water at a depth beyond 'which the effect of extraneous electrical waves of signaling frequencies employed in the cable is negligible, and the effect of disturbing electric' waves of such frequencies at lesser depths is made negligible by a )alanced relation of the main cable and its balancing return circuit,.with respect to the receiver, as pointed out in the Osborne patent just mentioned. The length of the core 6 required to carry thebalanced section of the cable out to an adequate depth of water may be considerable as indicated by the dotted portion of the twin core cable section 4. In the case of a cable between New York and the Azores, it has been found advisable to use a sea earth core about 100 miles in length at the western end of the cable.

The circuit 10, comprising conductors 13 and 14, may be, for example, a twin conductor or full metallic land cable having` a length of the order of 15, or 20 miles that is eX- posed to inductive interference from electric railroads and power lines (not shown) which it parallels. The dotted portion of circuit 10 is intended to indicate the considerable extent of the circuit. The circuit 10 may be similar to the circuit 10. Although in the drawing these circuits are shown as separate cables, theconductors 13 and 14 and the conductors of circuit 10 may all be in the same cable. The amplifier 2 is indica-ted as a four-stage ampli'er comprisingvacuum tubes 15, 16, 17 and 18 in tandem. An input transformer for tbe amplilier is indicated at 20. the cable and transformer 20 and blocks 22 to 24 between the various stages of the amplifier indicates any desired signal shap-V ing networks or elements, for instance networks of the general characterrof those illustrated in my U. S. Patents 1,586,970 and 1,586,972, both issued June 1, 1926. and British Patent. 153,357 to lVestern Electric Company, Limited, in connection with a circuit similar to that in which the networks are here shown.

The tube 18 comprises an anoce a cathQde 26 and a control electrode 2l, and

Block 19 between each ct the other tubes of the amplifier 2 has similar electrodes. A battery supplies cathode heating current for the tubes, and suace current is supplied to tubes 15- and 16 from a battery 85, to tube 17 from a bat-v tery and to tube 18 from al battery l1. The circuit of tube 18 includes an adjustable resistance Ll2 preferably of a magnitude 0i several thousand ohms and a resistance 43. rEhe resistance 48 is lor straightening the grid potential plate current characteristic of the tube 18, to reduce distortion, and is preferably of a magnitude of several hundred ohms, but may be omitted, it desired. One end oi a current path including the windings of relays 11, 11' and 21 is connected to a point on battery 41, wh-ich when no signals are being received is at the same potential as the junction oi the other end of the path withl resistance 4t2. This prevents battery l1 from sending current through the circuit of the windings of relays 11, 11 and 21, except when' received signals cause increases and decreases oli the space current oit tube 18, in which case a? considerable portion ot the current changes is permitted tor flow through the windings of the relays. Amplifier 2 may have a possible voltage amplification at some frequencies of the order of 25,00()V times, and therefore should be earthed locally through a connection o'tI suiiiciently low impedance to keep the amplifi'er at practically the same potential as its surroundings 'tor all frequencies high enough to permit an appreciable electrostatic ieed-back between various parts of the amplifier. Failure to so stabilize the amplifier is likely to cause it to'oscillate continuously. However, il this stabilization should be effected by earthing the cathcdes oi the ampliii'er directly, as is' customary with vacuum tube amplifiers, and the circuit 10 were conduct-ively connected to the amplifier, the circuit 10 would bennbalanced as regards the inipedance's betweeny earth and its conductors, afs conductor 14' would be connected to earth while conductor 18 would be connected to a point onfbatteryv i-1 and to earth througl'i resistances 4-2, t3l and the plate to cathode circuit of amplifier 18. this point having an impedance of about 1.000 ohms to earth. Consequently, voltages induced in conductors 13 and 14E, from electric railroads andV power lines whichI it parallels. would sendl currents through circuits of unequal impedances to earth. with the result that there wouldl appear .across the receiving instruments, in the receiving apparatus lf2, disturbing-voltages' which might have a material effect in masking the signals. v

To prevent undue disturbance causedl by the tendency of the amplifier 2 to oscillate and at the same time avoid interferenceV 0r masking effects resulting from unbalancing the circuit 10, the ampliiier cathodes are earthed locally, or through a short earth cable of low impedance as at 44E, and a relay 11 is interposed between the output oi the amplifier and the circuit 10. To provide tor varyingv currents in theV windings of any ot the relays 11, 11 and 21V wi-thout necessitating variations' in the windings ot the' others of these relays, a variable resistance l5 is connected in series with the windings ot' relay 11 and the variable resistance 46 is connected in shunt to those windings. These resistan'ces are so arranged that their variation produces no variation in the impedance with which the circuit constituted by those two re'sistances and the windings of relay 11 faces' its supply circuit; and a similar set ot resistances 4.7 and .t8 isA similarly. associated with the windings of relay 11'; and' a set oli resistances 49 and 50 is. similarly associated with the windings of relay 21. The relay 11 repeats signal elernfents represented by periods ot positive, negativ/'e and zero current flow. The armature isv` normally held in a central position corresponding to Zerosi'gnaling current, but when actuated by a positive signal in its winding it applies apositive volta-ge to line 10i from battery 55, vand when actuated' by a negativey signa it applies a'. negative voltage to line 10 from battery 5G. A resistance 57, indicated as variable in magnitude iis connected in shunt relation to line 10 in order that when the armature of relay 11 retu' -`ls to its neutral positionv after having afppl-i'ed either battery to the line '10, the charge remaining in the line will quickly disch-arge through the line shunt, thus avoiding the distortion of the signal which would result if' the entire charge on line 10 were compelledy to flow through the receiving apparatus 12. The resistance 57 depends on* the' capacity and resistance of line 110, and' alsovv on how much of the voltage of batteries 55.' andE 56 it is `permissible to sacrifice. In a certain case ai value oit'lOO ohms was found satisfactory. If desired, ay resistance 58l of the order ofV 10 ohms may be, connected in series lwith resistance 57 for supplying voltage tov a monitoring device 59' locall to they a'mplilier 2.

It will* be' noted that when the Vtongue ot the' relay 11 makes contact with either ol the battery connectors the voltage of the battery'is applied abruptly to the line and resistance 57 through the resistance 60 and one ofY `the battery protective resistances, but when thel relay tongue opens the connection the line discharges through its shunt resistance 57'. This results in the voltage applied to the line by the relaj)7 rising to its full' value' more rapidlyV than it falls when the contact opens and the line discharges through resistance 57, but il resistance 60 is given a suiciently large value,

the distortion or" the signal thus caused is reduced to a negligible amount. ln a certain case the resistance GO plus the battery protective resistance amounted to about one thousand ohms. Line l is associated with relay ll in s. c Q the manner in `rhichlinc l is associated with relay ll, sreiierably 'ith the employment of batterles, resistances and oscillograpli 59 corresponding to the batteries, resistances and oseillograph just described .in connection with line l0 and relay ll. llowever, the resistances cr'inectefl in series across the line l0 may be o L. value convenient 'for supplying current to aie monitoring device 59 since the relay ll need repeat only positive and negative immisesA iis thispermits the use ot a relay whose armature has only two positions ol' i. that is, with the armature tongue' against either ot its contacts, it is not necessary to provide means for discharging the line l0 while its armature is midway between contacts, as the line discharges through the battery and the travel time ot the armature is too short to permit appreciable signal distortion.

rhe relay 2l when employed as a Zero wander correcting relay, as referred to above, may be a three-element relay, the armature olr which vibrates through its midposition in response to current passing through its windings, but does not close either ot its contacts except when the signal current has added to it a low frequency component (commonly called Zero wander) of a magnitude at least as great as is to be permitted. lliis relay is therefore marginal in its operation and the provision et the re sistances 4:9 and 50 makes it possible to properly adjust the operating margin without changing the current flow through the windings ot relays ll and ll', or the impedance ot thc output circuit ot tube 18.

ln Fig. l the ainplilier input is connected lo the submarine cable and its balancing rcturu circuit by the transformer 20, the secondary winding ot which is surrounded by an electrostatic shield ot copper which is electrically connected to the terminal et the secondary winding that is connected to the amplilier cathodcs and the earth connection Alli. The transformer 20 prevents distmbancoy ol the balance bctwee the sea cable and its balancing return circuit by the earthing comiection ifiand therefore ijrcvents that earthii counec on Ylfroui adversely affecting the Yluncthoning of the balancing return circuit which is Vfor thc purpose elt diminishing interference due to action ot extraneous electric l'lelds upon the receiving end out cable l.

Fig. 2 shows a torni ot the invention in which the cable l is connected to the input oi an amplifier 2 which may be similar to the amplifier 2 of tigf l., but ai :out

transformer such as the transformer 2O of amplilier ldentical elements in the two figures are indicated by the same reference characters, and elements of Fig. 2 which are similar to elements ot Fig, l are lindicated. in l? ig. 2 bv the reference characters employed in Fig. 1,but with the addition of a prime marlr. y

To prevent undue disturbance resulting from the tendency oi the amplifier 2 to oscillate and at the same time avoid unbalancing the circuit l, the input of the amplilier, when connected to the cable l, is shunted by two condensers l0 and 7l oi? equal capacity connected in series and the junction et the two condensers is earthed locally through a low impedance sea earth cable, as at 72. Network 19 having thev same general character and function as network 19 ot Fig. l may be inserted between the grounded capacitative shunt circuits 70, 7l and the amplifier 2. rllhe capacity el the condensers TO, 7l should be suliiciently large so that the amplilier 2 with its cathodes earthed through condenser 7 l is sutliciently stabilized tor the frequencies which would otherwise cause oscillation. With the grounded condenser, shunt, the cable circuit l of Fig. 2 is still balanced. The connections from the shunt 70, ll-to the grid and the filament et the first tube of amplilier 2 may be conductive, no transformer such as transformer 2O ot Fig. l being required in Fig. 2. ln Fig. 2 the natural capacities to ground of the amplilier batteries (not all shown) corresponding to the batteries such as 30, 35, l0 and 4l of Fig. l, are not usually large enough to require that they be taken into account, although it is quite evident that this capacity is connected in parallel with condenser 7l.

lt in the system et Fig. 2 the circuit l0 w re connected to the amplifier 2 conductively instead of through relay ll vthe balance between conductor 5 ot the sea cable and its return conductor 6 would be destroyed, as conductor G would be connected directly to conductor lll of the land cable 10, which has a capacity to earth of several microitarads while conductor '5 would not have a similar direct connection to conductor i3. rlhe balance between conductors 13 and 14- olf the land cable l0 would similarly` be destroyed, conductor la being connected directly to conductor G, while conductor 1S is connected to conductor V6 only through an impedance of several thousand ohms.

This mutual unbalancing of the two cables would cause each to be seriously adected by extraneous electrical fields and the resulting induced voltages would interfere seriously with signaling.

The use ot relay ll prevents this connection and consequent imbalance.

a such that oil: 2% the direct from the system pedance to earth of the; amplifier' ends of cores 5 and 6 may beso` large. that it would, if the amplifier end of thefsea cable and its balancing return circuit were connected conducti vely to the cond uctorsl and ll .as symmetrically with respect tofthose conductors as 1 referred to above, exert upon the balance` o" the circuit l0 a cisturbingi effect met al, comparison to that which vthe cathodecapacitive earthing connection at Z2 would exert. The relay il between the circuit l0 and the amplifier prevents, each of these disturbing effects`A either of which might be serious.

In Fie. Q only one relay has been shownin thekoutp t circuit of tube "iSfinstead of three relays as in l.v However, it will be clear that the system of .2 may be arranged for multiplex operation and Zero wandercor- 'ecticn as is the system of Eig.`r 1 bythe addition of synchronizing .means 7and Zero wander correcting apparatus as indicatedl connection with Fig. 1,' point ofview, it will be clearl that the vsystem of Fig. l may. be modified by earthing the cathodes and connecting thev sea cableto the input of thel amplifier in the manner shown in Fig. 2 instead of in the manner shown in Fig. l. lt will also be cleary that, if desired.- tlie Zero ycorrecting means may .be omittted of; Fig. l, andV that so.. may also the synchronizing. apparatus where only the usual visual signaling by Vmeans of the Morse code is desired. l

`What is claimed is: D

l, In combination, a'circuit, of substantial length` balanced as regards the impedances of its tivo sidesto ear terference from extraneous elQCtiic lields, an electric space dischargel amplifierA of direct amplifying, non-duplex type. at one end of said circuit, said amplifier having a cathode with an earth,connection` of im# pedance sufficiently low to prevent said am,- plilier from oscillating, and a relay adjacent said amplifier interposed between said circuit and said amplifier and insulating said circuit from said amplifier so that said balance of said circuit is maintained, in order to minimize deleterious effects of said interference.

2,'A cable system, unbalanced with respect to ground and having a grounded sea earth return conductor.v feeding into a nonduplex direct amplifying amplifier having a grounded cathode, input inea-ns whereby differences of potential of signaling frequency (due to disturbances) between the sea earth y ground, and the cathode ground are amplified less by the amplifier than signaling waves of equal voltage applied to the ampliiier at the cable and sea earth conductor terminals, in combination with an output line for said amplifier having its sides balanced with respect to ground, and a relay connecting 'said amplifier and output line.

ork from another Y balanced as regards li. and exposed to inf" 3. A signaling system comprising an elec" tric space discharge ainpliiier of direct amplifying, non-duplex type havin@- cathode earthed through impedance suileciently low tojpreventsaid amplifier fronL oscillating and means transmitting lowA frequency telegraph `signals to said amplifieipf" ld means including a submarine cable, abalancing circuit therefor a 'ra- Ajed to reduce; rban'ces, and means preventing said cathode earthing connection from unbalancinfy said cable and Aits balancing circuit; said ein compris g' a transmission circuit of cub.- stantial len,D balanced as regards the iinpedances to earth of its conductorafand ielayadjacent said amplier, having an in@ put circuit and an. output circ' it insulated from each other, to relay the amplified ion',

frequency telegraph` signals to said, transi. signaling system. coi` pricing an, elec,- tric spacel dischargev amplierv of direct am? plifying, non-duplexV type, means transmit-` ting-low frequency telegraph signals tov said amplifier, said means including a long: submarinecable and a balancing circuit therefor' arranged to diminish disturbances, a

transmission circuit.l ofl substantial length.- tlie impedances to earth of its conductors andalso lecards their exposure "to extraneous ymagnetic iields, .and a relay adjacentsaidI amplifier having an. input circuit and an' output-circuit insulated from each other, for 'relaying Jthe amplified low. frequency telegraph rsignals `to saidv transmission circuitand also insulating the transmission circuit from the submarine cable and its `balancing conductor so :that the 'transmission circuit will not adversely affect thefunctioning-of the cablebalancing circuit in diminishing interference effects", and so that the cable and its balancing circuit will not disturb the balance of the impedance to earth of the conductors of the transmission circuit and vthereby increase effects of interference to which the latter circuit maybe exposed.

5. A signaling system comprising an electric space discharge amplifier of direct am plifying, non-duplex type, having a cathode element, means transmitting low frequency telegraph signals to said amplifier, said means including a long submarine cable and a balancing return circuit therefor arranged to diminish disturbances from sources eX- traneous to the system, a transmission circuit of substantial length, balanced as regards the impedaiices to earth of its conductors, a relay adjacent the amplifier, having an input circuit and an output circuit insulated l F ein lili.

from each other, for relaying the amplified low frequency telegraah signals to said transmissi n circuit and insulating the transmis sion circuit from the submarine cable and its return circuit to prevent the transmission circuit from adverselyaffecting the functioning ol the cable and its balancing return lcircuit in diniinishing interference effects and to prevent the cable and its balancing return circuit from disturbing the balance ofthe impedances to earth of the conductors of the transmission circuit and thereby increasing effects of' interference to which the latter circuit may be subjected, and similar' impedances connected in serial relation across the amplifier end of said submarine cable and its balancing' return circuit, said cathode element being connected to ear th through at least one of' said similar impedances and only in such lmanner that the impedances ofl said cable and its balancing return circuit remain balanced so that the Cable and its balancing return circuit maintain their efliciency in diminishing interference effects.

6. A system according to claim 5, said similar impedances having such values as to shunt from said amplifier a small part only of the currents of signaling frequencies.

7. A system according to claim 5, said similar impedances consisting principally of capacitative reactance.

8. A system according to claim 5, said similar impedances consisting principally of capacitative reactance and having such values as to shunt from said amplifier a small part only of currents of frequencies from zero to several hundred cycles per second.

9. In a submarine cable signaling system,

a submarine cable, an electric space discharge receiving' amplifier therefor having an output circuit, a line for retransmitting signals received over said cable, a line for transmitting synchronizing impulses generated by the signals received over said cable, a plurality of relays, each of said relays having windines included in said circuit, one of said relays repeating signals to said signal transmitting line, and another of said relays repeating synchronizing impulses to said other line, a resistance in series with said windings of each of said relays, a resistance in shunt to said windings, and means for varying said resistances in such manner to maintain constant the value of the impedance presented by the circuit consisting of said latter windings and said resistances.

l0. A relay and batteries for repeating telegraph signals constituted by elements of positive, negative or zerol voltage, a line toitransmitting said signals, a resistance shunting said line for permitting the charge received thereby to be discharged at the termination of a positive or negative impulse, and a resistance in seriesV between said bratteries and said line shunt, proportioned so as to make the time of building upof the volt# tage on the line approximately equal to the time in which said Voltage is discharged, whereby signal distortion is reduced.

ll. n a submarine cable signaling fsystem, an electric space discharge receiving amplilier having an output circuit, a 'plurality of relays having windings in said output circuit, one of said relays repeatingsignalsV to a line circuit, another ofl said relays repeating synchronizing impulses to another line circuit-l. and another of said relays re" peating zero wander impulses. i

.12. A submarine cable signaling system comprising an electric space discharge receiving amplifier havingv an output circuit, two relays having their operating windings connected in said output circuit, receiving apparatus and synchronizing apparatus, `and separate circuits each extending 'from one of' said relays to the receiving apparatus and synchronizing apparatus respectively.

In wit-ness whereof, I hereunto subscribe my name this lst day of December, A. D.,

AUsTEN M. oURTrs. 

